Download The star formation history of galaxies in 3D: CALIFA perspective

Galaxies in 3D across the Universe
c International Astronomical Union 2015
Proceedings IAU Symposium No. 309, 2014
B. L. Ziegler, F. Combes, H. Dannerbauer, M. Verdugo, eds.
doi:10.1017/S1743921314009399
The star formation history of galaxies in 3D:
CALIFA perspective
R. M. González Delgado1 , R. Cid Fernandes2 , R. Garcı́a-Benito1 ,
E. Pérez1 , A. L. de Amorim2 , C. Cortijo-Ferrero1 , E. A. D. Lacerda2 ,
R. López Fernández1 , S. F. Sánchez1,3 , N. Vale Asari2 and CALIFA
collaboration
1
Instituto de Astrofı́sica de Andalucı́a (CSIC), Glorieta de la Astronomı́a s/n, E-18008
Granada, Spain
email: [email protected]
2
Departamento de Fı́sica, Universidade Federal de Santa Catarina, P. O. Box 476, 88040-900,
Florianópolis, SC, Brazil
3
Instituto de Astronomı́a,Universidad Nacional Autonóma de Mexico, A. P. 70-264, 04510,
México,D. F.
Abstract. We resolve spatially the star formation history of 300 nearby galaxies from the
CALIFA integral field survey to investigate: a) the radial structure and gradients of the present
stellar populations properties as a function of the Hubble type; and b) the role that plays the
galaxy stellar mass and stellar mass surface density in governing the star formation history and
metallicity enrichment of spheroids and the disks of galaxies. We apply the fossil record method
based on spectral synthesis techniques to recover spatially and temporally resolved maps of
stellar population properties of spheroids and spirals with galaxy mass from 109 to 7×101 1 M .
The individual radial profiles of the stellar mass surface density (μ ), stellar extinction (AV ),
luminosity weighted ages (logageL ), and mass weighted metallicity (logZ/Z M ) are stacked
in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc and Sd). All these properties show
negative gradients as a sight of the inside-out growth of massive galaxies. However, the gradients
depend on the Hubble type in different ways. For the same galaxy mass, E and S0 galaxies show
the largest inner gradients in μ ; and Andromeda-like galaxies (Sb with log M (M ) ∼ 11)
show the largest inner age and metallicity gradients. In average, spiral galaxies have a stellar
metallicity gradient ∼ -0.1 dex per half-light radius, in agreement with the value estimated for
the ionized gas oxygen abundance gradient by CALIFA. A global (M -driven) and local (μ driven) stellar metallicity relation are derived. We find that in disks, the stellar mass surface
density regulates the stellar metallicity; in spheroids, the galaxy stellar mass dominates the
physics of star formation and chemical enrichment.
Keywords. galaxies: evolution – galaxies: formation – galaxies: fundamental parameters –
galaxies: stellar content – galaxies: structure
1. Introduction
Much of we know about galaxy properties has come from panoramic imaging or 1D
spectroscopic surveys. While imaging provides useful 2D information of galaxy morphology and structural properties, spectroscopic surveys give information on the central or
global stellar population and ionized gas properties and kinematics. However, galaxies
are a complex mix of stars, interstellar gas, dust and dark matter, distributed in their
disks and bulges, and resolved spatial information is needed to constrain the formation
processes and evolution of the galaxy sub-components.
Integral Field Spectroscopy (IFS) observations can provide a unique 3D view of galaxies
(two spacial plus one spectral dimensions), and allows to recover 2D maps of the stellar
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R. M. G. Delgado et al.
population and ionized gas properties, and kinematics. Until very recently it was not
possible to obtain IFS data for sample larger than a few tens of galaxies. ALTAS3D
(Cappellari et al. 2011), CALIFA (Sánchez et al. 2012), SAMI (Croom et al. 2012) and
MaNGA (Bundy et al. 2014) surveys are the first in doing this steep forward, taking
observations of several hundreds to several thousands of galaxies of the nearby Universe.
CALIFA is our currently-ongoing survey, observing 600 nearby galaxies with the PPaK
IFU at the 3.5m telescope of Calar Alto observatory. The observations cover 3700-7000
Å with an intermediate spectral resolution (fwhm ∼ 6 Å in the data presented in this
contribution) and ∼1arcmin2 field of view with a final spatial sampling of 1 arcsec.
Galaxies were selected from SDSS in the redshift range 0.005 z 0.03, covering all
the color magnitude diagram down to Mr -18, resulting in a sample containing all
morphological types. An extended description of the survey, data reduction and sample
can be found in Sánchez et al.(2012), Hussemann et al.(2012) and Walcher et al.(2014).
Previously, we derived the spatial resolved star formation history of the CALIFA galaxies on the first data release (DR1) using the fossil records that the stellar populations
imprint in the galaxy spectra. This method dissects galaxies in space and time providing
a 3D information that allows to retrieve when and where the mass and stellar metallicity were assembled as a function of look-back-time. We use the STARLIGHT code
(Cid Fernandes et al.2005) to do a λ-by-λ spectral fit using different sets of single stellar
population (SSP) models. These SSP are from a combination of Vazdekis et al. (2010)
and Gonzáles Delgado et al.(2005) (labelled GM e), or from Charlot & Bruzual (2007)
(labelled CBe).
Our scientific results from the first 100 CALIFA galaxies were presented in Pérez
et al.(2013), Cid Fernandes et al.(2013, 2014) and Gonzáles Delgado et al.(2014a). One
highlight result of these works is that the signal of downsizing is spatially preserved,
with inner and outer regions growing faster for more massive galaxies, consequence of
the inside-out growth of massive galaxies.
Here, based on the fossil records analysis of 300 CALIFA galaxies we present the results
on: a) the radial structure and gradients of the stellar populations as a function of the
Hubble type; and b) the role that plays the galaxy mass and stellar mass surface density
in governing the star formation history and metallicity enrichment in ellipticals and in
the bulge and disk components of galaxies.
Two complementary contributions to this one are presented in these proceedings:
Sánchez presents CALIFA survey in the context of other contemporaneous IFS surveys
such as SAMI and MaNGA; and Cid Fernandes et al. explains in details the methodology
that we apply here, the uncertainties associated to the method, and results related with
the growth of mass and metallicity in galaxies and their evolution.
2. Results
We present new results based on the radial structure of the present stellar population
properties of 300 CALIFA galaxies that were observed with the V500 and V1200 setups
and calibrated with the new pipeline 1.4 (see Garcı́a-Benito et al. 2014 for details). 1D
spatial radial profiles are obtained from the 2D maps, with an azimuthal averaging by an
elliptical xy-to-R conversion. These 2D maps are created after collapsing the SFH in the
time domain. The results are presented by stacking each galaxy individual radial profiles
that has been previously normalized to a common metric that uses the half-light-radius
(HLR) of each galaxy.
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The star formation history of galaxies in 3D: CALIFA perspective
101
2.1. Hubble sequence: stellar population properties of galaxies in the tuning-fork diagram
One step to understand how galaxies form and evolve is classifying galaxies and studying
their properties. Most of the massive galaxies in the near Universe are E, S0 and spirals
(Blanton & Moustakas 2009), following well the Hubble tuning-fork diagram. The bulge
fraction seems to be one of the main physical parameters that produce the Hubble sequence, increasing from late to early spirals. In this scheme, S0 galaxies are a transition
class between the spiral classes and the elliptical one, with large bulges, but intermediate between Sa and E galaxies. On the other hand, galaxies properties such as color,
mass, surface brightness, luminosity, and gas fraction are correlated with the Hubble type
(Robert & Haynes 1994). This suggests that the Hubble sequence can illustrate possible
paths for galaxy formation and evolution. If so, how is the spatial resolved stellar population properties of galaxies correlated with the Hubble type? Can the Hubble-tuning-fork
scheme be useful to organize galaxies per galaxy mass and age or galaxy mass and metallicity?
CALIFA is a suitable benchmark to address these questions because it includes a significant amount of E, S0 and spirals. After a visual classification, the 300 galaxies were
grouped in 41 E, 32 S0, 51 Sa, 53 Sb, 58 Sbc, 50 Sc, and 15 Sd. This sub-sample is a
well representation of the morphological distribution of the whole CALIFA sample. Here
we present the radial structure of the stellar mass surface density (μ ), stellar extinction (AV ), luminosity weighted stellar age (logageL ), mass weighted stellar metallicity
(logZ/Z M ), by stacking the galaxies by their Hubble type. First, we present how
galaxies are distributed by stellar mass (M ) and their sizes in mass (aM
50 : radius that
contains half of the mass) and in light (aL50 : radius that contains half of the light, HLR).
Most of the results discussed here are obtained with the GM e SSP models, but similar
results are obtained with the CBe base (see Fig.1).
Galaxy stellar mass: We obtain the galaxy stellar mass (M ) after resolving spatially
the SFH of each zone and hence, taking into account spatial variation of the stellar
extinction and M/L ratio. Fig.1a shows the distribution of M as a function of Hubble
type. The mass ranges from 109 to 7×1011 M (GM e). We see a clear segregation in
mass: galaxies with high bulge -to-disk ratio (E, S0, Sa) are the most massive ones (
1011 M ), and galaxies with small bulges (Sc-Sd) have masses M 1010 M . The galaxy
stellar mass distribution obtained with CBe models is similar to M with GM e base,
but shifted by -0.25 dex due to the change of IMF (Chabrier with GM e and Salpeter
with GM e SSP models)
Galaxy size: We take the advantage of our spatially resolved SFH and extinction
maps to show that galaxies are more compact in mass than in light (González Delgado et al. 2014a), resulting in a ratio of the radius that contains half of mass with
L
respecto to the ratio that contains half of the light (aM
50 /a50 ) of 0.8. Galaxies are therefore typically 20% smaller in mass than how they appear in optical light. Fig.1b shows
L
the distribution of aM
50 /a50 as a function of Hubble type, and a clear trend is observed.
L
Sa-Sb-Sbc have the lowest aM
50 /a50 , due to the fact that they show a very prominent
old bulge which have similar central properties to the spheroidal components of S0
and E, but a blue and extended disc which contributes to the light in the range Sa to
Sbc.
Stellar mass surface density: The left panel in Fig.2 shows the radial profiles (in
units of aL50 ) of log μ obtained with GM e SSP base. Individual results are stacked
in seven morphological bins. Error bars in the panel indicate the dispersion at one aL50
distance in the galaxies of the Sa class, but it is similar for other Hubble type and radial
distance. Negative gradients are detected in all galaxy types and increase from late type
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R. M. G. Delgado et al.
Figure 1. Left: Distribution of the galaxy stellar masses obtained from the spatially resolved
spectral fits of each galaxy for each Hubble type of the galaxy of this work (grey small points).
The coloured dots and stars are the mean galaxy stellar mass in each Hubble type obtained with
the GMe and CBe SSP models. The bars show the dispersion in mass. Right: Relation between
L
aM
5 0 /a5 0 and Hubble type. Symbols are as in the left panel of the figure.
Figure 2. Radial profiles of the stellar mass surface density (in logarithm scale, log μ ) and
the stellar extinction AV as a function of Hubble type. The radial distance is in HLR units.
(Sd) to early type (S0, and E) galaxies. At a constant M , spheroidal (S0 and E) are more
compact than spirals, and S0 and E galaxies have similar compactness at all distances.
Stellar extinction: The right panel in Fig.2 shows the radial profiles AV . All galaxy
types show radial profiles that increase toward the center. Early type galaxies (E, and
S0) are also extinguished toward the nucleus by 0.2-0.4 mag, while out of 1 HLR of
the galaxies, the (old) stellar population are almost reddening-free. All spiral disks show
∼0.2-0.3 mag extinction. The bulges are significantly more extinguished up to 0.6 mag,
except the bulges of late type spirals (Sd) that AV is similar to the extinction in the disk.
Stellar ages: The left panel of Fig.3 shows the radial profiles of logageL (in yr). Symbols are as in Fig.2. Negative gradients are detected for all the Hubble types, suggesting
that the quenching is progressing outwards, and the galaxies are growing inside-out, as
we concluded with our mass assembly growth analysis (Pérez et al. 2012). Inner gradients
are calculated between the galaxy nucleus and at 1 aL50 , and the outer gradient between
1 and 2 aL50 . The inner age gradient shows a clear behaviour with Hubble type, being
maximum for spirals of intermediate type (Sb-Sbc). At M constant, Sb-Sbc galaxies
have the largest age gradient. The age gradient in the outer disk (between 1 and 2 aL50 )
is smaller than the inner ones, but again it is larger for the spiral Sa-Sb-Sbc.
Stellar metallicity: The right panel in Fig.3 shows the radial profiles of mass weighted
stellar metallicity obtained as explained in González Delgado et al.(2014b). Except for
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The star formation history of galaxies in 3D: CALIFA perspective
103
Figure 3. As in Fig.2 for the luminosity weighted ages and the mass weighted metallicity.
late spirals (Sc-Sd), spirals present negative gradients in average ∼ -0.1dex per HLR,
similar to the value obtained for the nebular oxygen abundances obtained by CALIFA
(Sánchez et al. 2013). For galaxies of equal stellar mass, the intermediate type spirals
(Sbc) have the largest gradients. These negative gradients again are sights of the insideout growth of the disks. However, the metallicity gradient for late spirals is positive
indicating that these galaxies, in the low mass galaxy bins, may be formed from outsidein. This result is also in agreement with our results from the mass assembly evolution
(Pérez et al. 2012).
2.2. The role of μ and M in the SFH and chemical enrichment of galaxies
The galaxy stellar mass is also considered one of the fundamental properties as it also
provides a measure of the galaxy formation and and evolution. The bimodal distribution
of galaxies in the color-magnitude diagram that place them in the red sequence and
blue cloud not only reflects the Hubble type, but also the dependence of the distribution
on the galaxy stellar mass. Sorting galaxies by M we can study how their properties
scale among the different classes. With CALIFA, thanks to the spatial information, we
can check how important are the local (μ - driven) and global (M -driven) processes in
determining the star formation history and chemical enrichment in galaxies.
We find that there is a strong relation between the local values of μ and the metallicity
which is similar in amplitude to the global mass metallicity relation that exits between
logZ/Z M and M over the whole 109 to 1012 M range (González Delgado et al.
2014b). This means that local and global processes are important in the metallicity
enrichment of the galaxies. However, the balance between local and global effects varies
with the location within a galaxy. While in disks, μ regulate the stellar metallicity,
producing a correlation between log μ and logZ/Z M , in bulges and ellipticals is M
who dominates the chemical enrichment (Fig.4). Furthermore, in spheroids the chemical
enrichment happened much faster and earlier than in disks.
These results are in agreement with the analysis of the star formation history of galaxies (González Delgado et al. 2014a). We have shown that mean stellar ages (a first
moment descriptor of the SFH) relate strongly to μ in galactic disks, indicating that
local properties dictate the pace of star-formation. The slower growth (hence younger
ages) found at low μ should lead to less metal enrichment, in agreement with the μZR
realtion. Within bulges/spheroids, M is a much more relevant driver of the SFH. Most
of the star formation activity in these regions was over long ago, leading to fast metal
enrichment and little or no chemical evolution since those early days.
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R. M. G. Delgado et al.
Figure 4. Left: Local stellar metallicity versus the local stellar mass surface density. The grey
circles tracks the μ -binned stellar metallicity relation (μZR). Blue circles show the μZR obtained
considering only star younger than 2 Gyr in the computation of the metallicity. Cyan stars show
the CALIFA-based nebular μZR of Sánchez et al.(2013). Middle and right: The mean μZR
obtained by breaking the 300 galaxies sample into five M intervals, restricting the analysis to
spatial regions outwards and for the inner R= 0.5 HLR
Acknowledgements
This contribution is based on data obtained by the CALIFA survey (http://califa.caha.es),
funded by the Spanish MINECO grants ICTS-2009-10, AYA2010-15081, and the CAHA
operated jointly by the Max-Planck IfA and the IAA (CSIC). The CALIFA Collaboration
thanks the CAHA staff for the dedication to this project. Support from CNPq (Brazil)
through Programa Ciência sem Fronteiras (401452/2012-3) is duly acknowledged.
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